Cassidy, a doctor who still practices, was leading Landrieu, 65 percent to 35 percent when the Associated Press called the race 30 minutes after polls closed. Republicans also retained two House seats in additional runoff races. Landrieu has a history of winning races that seemed unwinnable. But this time, she was overwhelmed by the GOP wave that gave Republicans seven seats on election night. Landrieu and Cassidy were forced into a runoff after neither secured 50 percent of the vote, as Louisiana requires, to win outright.

The extended campaign created problems for Landrieu. Democrats no longer had any hope of taking a majority in the Senate, and her race became something of a postscript. The Democratic Senatorial Campaign Committee pulled its ad reservations in support of Landrieu. Republican groups outspent Democratic groups in the runoff by monumental proportions, accounting for 97 cents of every dollar spent on the race, according to The Associated Press.

Landrieu also lost a major part of her argument for re-election: clout. In the general election, she pointed often to her chairmanship on the Energy and National Resources Committee, and how that put her in a position to help the oil industry — a crucial economic driver in Louisiana. But with Republicans in control, she would have been relegated to ranking member.

Republican focused on tying Landrieu to President Barack Obama, an unpopular figure in the state. It worked.

Cassidy's win marks the end of the 2014 Senate campaign season, and gives Republicans 54 seats in their new majority which gavels in next month.

Abraham led Mayo, 66 percent to 34 percent, with two out of 845 precincts reporting when the AP called the race.

Voters cut McAllister's tenure in the House short last month, when he came in fourth in the all-party ballot. In Louisiana, all candidates run on the same ballot on Election Day, with a runoff called if no candidate passes the 50 percent threshold.

McAllister first won his seat in this northeastern Louisiana district in a special election in November 2013. But just a few months later, surveillance footage surfaced of a married McAllister kissing a married staffer in his district office. McAllister picked up the "Kissing Congressman" nickname, and the scandal dogged his re-election bid.

Abraham's win was nearly a foregone conclusion. GOP presidential nominee Mitt Romney carried the district by a 23-point margin in 2012.

Graves defeated Edwards, 66 percent to 34 percent, when the AP called the race about 20 minutes after polls closed.

Graves succeeds Cassidy, who vacated this Baton Rouge-area House seat to run for Senate against Landrieu.

Edwards is a storied political figure in Louisiana, having spent decades in the governor’s mansion before a corruption scandal landed him in federal prison for eight years.

Despite his prominence in the state, Saturday’s runoff was seen as largely a formality for a Graves victory. The district voted for GOP presidential nominee Mitt Romney by a 34-point margin in 2012, making it a safe Republican seat.

Edwards only made the runoff thanks to a crowded GOP field that splintered the Republican vote.